Regulating Dendrite‐Free Zinc Deposition by Red Phosphorous‐Derived Artificial Protective Layer for Zinc Metal Batteries

Abstract Rational architecture design of the artificial protective layer on the zinc (Zn) anode surface is a promising strategy to achieve uniform Zn deposition and inhibit the uncontrolled growth of Zn dendrites. Herein, a red phosphorous‐derived artificial protective layer combined with a conductive N‐doped carbon framework is designed to achieve dendrite‐free Zn deposition. The Zn–phosphorus (ZnP) solid solution alloy artificial protective layer is formed during Zn plating. Meanwhile, the dynamic evolution mechanism of the ZnP on the Zn anode is successfully revealed. The concentration gradient of the electrolyte on the electrode surface can be redistributed by this protective layer, thereby achieving a uniform Zn‐ion flux. The fabricated Zn symmetrical battery delivers a dendrite‐free plating/stripping for 1100 h at the current density of 2.0 mA cm–2. Furthermore, aqueous Zn//MnO2 full cell exhibits a reversible capacity of 200 mAh g–1 after 350 cycles at 1.0 A g–1. This study suggests an effective solution for the suppression of Zn dendrites in Zn metal batteries, which is expected to provide a deep insight into the design of high‐performance rechargeable aqueous Zn‐ion batteries.

tube and the sealed quartz tube put into a tube furnace, and then it was heated to 500 o C with a rate of 2 °C min -1 for 4 h under Ar atmosphere. Subsequently, the temperature was cooled down to 260 o C and kept for 2 h to convert white P to RP, while the cooling rate was 1 o C min -1 .
Finally, the as-prepared product was obtained after cooling down to room temperature.
Preparation of Zn@RP-NC, Zn@NC, Ti@RP-NC, and Ti@NC: At first, Zn foil with a thickness of 0.02 mm was sonicated in ethanol to clean the surface. For Zn@RP-NC anode, a slurry of RP/NC and polyvinylidene fluoride (PVDF) in N-methylpyrrolidone (NMP) was employed onto the Zn foil by a slurry coating method and dried at 60 °C in a vacuum oven for 12 h. As a comparison sample, the Zn@NC was prepared by the same method. A similar method was used to prepare Ti@RP-NC and Ti@NC with Ti foil (0.02 mm thickness).

Preparation of MnO2:
In a typical synthesis, MnSO4·H2O (0.67 g) and (NH4)2S2O8 (0.91 g) were added to DI water and stirred for 1 h. After that, the solution was heated at 140 o C for 14 h. Finally, the as-prepared product was washed with DI water and ethanol individually. The MnO2 electrode was fabricated via the slurry coating method. The MnO2, super-P, and PVDF with a mass ratio of 75:15:10 were added in NMP to form a homogeneous slurry, which was then coated onto the Ti foil and dried at 60°C for 12 h in a vacuum oven. The Ti foil was punched into circle disks with a diameter of 12 mm. The MnO2 loading for each disk was controlled around 0.45-0.55 mg.
Material Characterization: Micro-morphologies of materials and electrodes were observed by using a field-emission scanning electron microscope (FE-SEM; MERLIN (Carl Zeiss)) and a transmission electron microscope (TEM; FEI Talos F200i). The energy-dispersive X-ray spectroscopy (EDS) was utilized to detect the elements. The 3D morphology and surface roughness were characterized by confocal laser microscopy (KEYENCE VK-X200). The were evaluated by the X-ray photoelectron spectroscopy (XPS, K-alpha (Thermo Electron)).
Binding energy corrections were made to the raw spectra by using the C 1s peak at 284.6 eV.
The Zn dendrite growth was in-situ observed by using an optical microscope.

Fabrication of Batteries and Electrochemical Measurements:
The symmetrical cells were assembled to investigate the electrochemical behavior of the pristine Zn, Zn@RP-NC, and Zn@RP-NC electrodes. The electrode was cut into discs with a diameter of 12 mm. The electrolyte was 2 M ZnSO4 solution. Glass fiber as a separator was employed to assemble standard two-electrode Swagelok cell. The same electrolyte was used in each battery to get standard test results. Cyclic voltammetry (CV) curves of Zn plating/stripping were measured at a scan rate of 5 mV s -1 in a three-electrode system consisting of Ti plate, Zn plate, and Ag/AgCl          Table S1. Cycling performance of some Zn symmetric batteries by modification of interfacial layer with different strategies.

Zn/Sn(200)
Chemical displacement reaction 0.5 1.0 500 [10] In-coated Zn Ion-exchange 1.0 1.0 300 [11] 4.0 1.0 400 Zn|In Spontaneous galvanic replacement 1.0 1.0 520 [12] Zn(002) Large rolling deformation 1.0 1.0 500 [13] 502 glue coated Zn Spin-coating 2.0 1.0 400 [14] Stratified deposition framework redox reaction +sputter 2.0 1.0 1000 [15] Zn@ZnP-NC Slurry coating      The diffusion coefficient (D) can be calculated based on the following equation: where τ is the duration of the current pulse time, mB. MB, and VM denote the active mass, molar mass, and molar volume of electrode material, respectively. S is the electrode-electrolyte interface area and ΔEs is the quasi-thermodynamic equilibrium potential difference between before and after the current pulse regardless of the IR-drop. ΔEτ represents the change of voltage during the current pulse. [16]